how's it hanging

We've got a discussion in the works on our Facebook page about the phrase "how's it hanging?" that I thought I'd bring to the blog as well. What's the deal with how's it hanging? (Asked in my best Jerry Seinfeld voice, of course.) Is it sexist? Does it refer to a dangling penis, or is it just a way to say hey? And what other slang terms are we using that are secretly SEXUAL? It's open thread time!